Maybe your hair has always been on the thin side. Or maybe it’s lost its fullness as you’ve gotten older. (Yes, hair ages, too. Sigh.) Either way, there’s only so much that backcombing and volumizers can do. More and more, women are turning to hair supplements to give their roots a boost from the inside. Some experts recommend certain vitamins and targeted oral treatments supported by promising research and positive real-world results.

Can you really get gorgeous hair by popping a pill? We looked at five popular options to see what works and what may leave you—and your hair—flat.

Viviscal

This Scandinavian supplement contains silica (horsetail plant extract), vitamin C and a fish protein, and is one of the only ones that Doris Day, M.D., a celebrity dermatologist in New York City, recommends to her patients. “I’ve observed it help with hair thickness and regrowth, especially around the temple area,” she says. You take it twice a day for the first three months and then once a day after that.

David Babaii, a celebrity hair stylist, is a fan of the product, too, and often recommends it to his high-profile clients. He first noticed that it worked after seeing promising results on a client. “Within a month, I noticed growth of new hair and after six months, her hair was even thicker than before she started taking it,” says Babaii, who started taking the supplements himself after a major surgery caused his hair to thin out.

Biotin

Some research suggests that biotin (part of the B complex vitamins) may improve brittle nails and thinning hair. Many experts recommend a biotin supplement for hair health because it’s water-soluble (meaning your body excretes what it doesn’t need) and doesn’t have any side effects. In other words: Why not? “I have some very happy patients taking biotin right now,” says Day. “Even though the data is mixed, there’s at least enough to support trying it out.”

Vitamin D

The sunshine vitamin is important for a number of body functions (like aiding in calcium absorption), but experts are exploring the role it may play in hair health as well. “The vitamin D receptor helps regulate your hair cycle,” says Paradi Mirmirani, M.D., a dermatologist at the Permanente Medical Group in Vallejo, California, who recommends a supplement to her patients if their levels are low. (Your doc can give you a quick blood test to assess).

Experts aren’t sure exactly how the level of vitamin D in your body directly influences your hair growth, but many still think it’s a good idea to take vitamin D to ensure that your body has what it needs to sprout healthy, strong strands. “It’s very hard to get enough vitamin D through natural exposure if you apply sunscreen daily, so I often suggest a supplement just to be safe,” Day agrees.

Saw Palmetto Extract

This herbal remedy is processed from fruit of the American dwarf pine tree and may have some benefit for your hair, says Mirmirani. A small study found that 60 percent of patients who took a saw palmetto extract supplement said that their hair growth improved compared to just 10 percent of people taking a placebo.

Vitamin A

This antioxidant is often used in general hair, skin and nail supplement formulas because it is involved in skin regeneration, and is included in multivitamins for its benefits to vision and immunity. While it’s important to get enough vitamin A, too much can be dangerous. It is fat-soluble, which means that whatever your body doesn’t use each day builds up in your tissues. Going over the recommended daily intake can be harmful to your liver, cause fatigue and nausea as well as—ironically—hair loss. Make sure you read your vitamin labels and avoid taking multiple doses so you don’t over do it.

Healthy Diet

At the end of the day, no supplement can beat getting what you need the natural way. “Eating a healthy diet filled with wholesome foods is your best bet for gorgeous hair,” says Katherine Brooking, R.D., co-founder of appforhealth.com.

“Certain vitamins, like B6, B12 and folate, help with the creation of red blood cells, which in turn carry oxygen and nutrients to the body's cells and can help the scalp and growing hair,” she says. Iron (from lean beef, turkey, chicken, pork, shrimp, egg yolks and beans) helps those red blood cells do their job.

You can get your B12 from shellfish, salmon, and low-fat and fat-free dairy. Whole grains, lean protein, beans, nuts, lentils and leafy greens are great sources of vitamin B6. For folate, go for lentils, soybeans and many leafy greens. And don’t forget to eat enough protein. This macronutrient is important for cell growth and also provides structure for the hair.

Just remember

You can’t replace a bad diet with supplements. So it’s better to use a combo approach. Focus on improving your diet and talk to your doctor or dermatologist about vitamins and supplements that may be right for you.